Damp and moisture meters
Why is condensation a different finding from a failed damp-proof course?
Condensation is moisture from indoor air settling on a cold surface. A failed damp-proof course would be water from the ground getting past the layer that should stop it. Black mould on a cold external wall does not, by itself, prove the course has failed.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Kitchens, bathrooms and bedrooms often put a lot of water into the air. If that air meets a cold bit of wall or glass, it condenses. The mark is often mould on the surface, worse in winter, and not a salty tide mark. A damp-proof course sits near the base of the wall. It is not a ventilation system, and a ventilation fan is not a new damp-proof course.
A home survey can note mould, a cold wall and whether a fan or a trickle vent was seen. It cannot run the house through a heating season. Government guidance on damp and mould tells housing providers to find the cause. It does not tell a buyer to inject the wall because a bedroom wall is mouldy. Ask what else was damp at low level, away from the cold spots.
What should you ask your surveyor?
- Was the mould on cold surfaces, or was there a tide mark and salts at skirting level?
- What ventilation could you see: fans, vents, or windows that do not open?
- Are you separating a lifestyle and fabric issue from a failure of the damp-proof course?
What are the typical next steps?
- Do not commission an injected damp-proof course for mould on a cold wall.
- Note how the house is heated and ventilated before you blame the course.
- If the report still suspects moisture from the ground, ask for that suspicion to be separated in writing from the mould.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Will a dehumidifier fix a failed damp-proof course?
No. It can dry the air for a while. It does not rebuild a course or stop a leak.
Can a new kitchen cause condensation the surveyor did not see in summer?
Yes. A dry inspection day does not prove the winter pattern. Say so to anyone quoting from one visit.